The present invention generally relates to digital video signal transmitting apparatuses, and more particularly to an apparatus which stores a digital video signal into a memory device (hereinafter simply referred to as a memory) having a small memory capacity and reads out the stored digital video signal to transmit the digital video signal.
A recording and reproducing system has been proposed wherein a digital video signal and a digital audio signal are recorded onto a rotary recording medium upon recording. The digital video signal is obtained by subjecting a video signal to digital pulse modulation such as pulse code modulation (PCM), and the digital audio signal is similarly obtained by subjecting an audio signal to digital pulse modulation. Upon reproduction, the recorded signal is reproduced from the rotary recording medium, and an analog audio signal is obtained from the reproduced signal to reproduce the analog audio signal as reproduced sound while an analog video signal is obtained from the reproduced signal to reproduce the analog video signal as still picture, for example. Such a recording and reproducing system is being reduced to practice.
In the above described system, a signal corresponding to one frame of the reproduced digital video signal is stored into a memory (a so-called frame memory), and the stored signal is read out from this memory to be subjected to digital-to-analog conversion. The converted signal is supplied to a television receiver, and reproduced as a still picture. In this type of a conventional digital video signal transmitting apparatus, signals corresponding to all picture elements on a screen for one frame of video information are stored in the memory. Accordingly, even if a composite synchronizing signal, color burst signal, and the like are not stored into the memory, the memory still must have a considerably large memory capacity. Therefore, an expensive memory must be used, and there was a disadvantage in that the cost of the digital video signal transmitting apparatus as a whole became high.
Hence, a method was tested according to which a signal corresponding to one field within one frame of the reproduced digital video signal is stored into a memory (a so-called field memory), and the stored signal is repeatedly read out from this memory, to obtain one frame of reproduced still picture signal from the identical signals of two fields thus read out from the memory. According to this method, the memory only requires a memory capacity for one field, and may be manufactured at a lower cost compared to the one frame memory described before. However, according to this method, the video information is only stored for every other lines (horizontal scanning lines) within the picture of one frame. Thus, there was a disadvantage in that the vertical resolution of the reproduced picture became degraded to one-half.